the first "水准"generally describe the skills and machine…

提高中文水平

Linguistically, they are both correct. Forget about all the comments previously you saw, they are WRONG regarding to COMMONNESS. To judge commonness, there must be CONTEXT. In fact, in Taiwan and Southeast Asia (Malaysia and Singapore), "水准" is very commonly used as the synonym of "水平". You are absolutely correct if you say "提高中文水准" in these regions. Chinese is poetic language, and it can vary its meaning in application. Don't fuss about which phrase is "more correct". As a foreigner, without the framework of old habits, you can even create phrases from existing words (of course, you cannot create words, just like that we cannot create another alphabet and insert it into Latin). So long as people can understand you, who cares? Probably the next hot popular word could be from your invention, who can tell?

朋友們，感謝你們的幫助。

Sorry, I put the answer here just now. I cannot delete but edit it. Please ignore.